1. Field of the Invention
The present invention relates to an ultrasonic sensor equipped in a robot and adapted to detect objects, and more particularly to a scanning apparatus associated with such an ultrasonic sensor, capable of freely varying a scanning frequency of the ultrasonic sensor and accurately detecting the direction that the ultrasonic sensor is oriented.
Also, the present invention relates to a method for detecting objects by use of an ultrasonic sensor scanning 5 apparatus of the above-mentioned type, capable of accurately detecting all objects positioned in a search area, without a failure.
2. Description of the Prior Art
Generally, ultrasonic sensors are equipped in robots and used for detecting objects positioned along a robot travel path. Such ultrasonic sensors are adapted to convert a pulse signal into an ultrasonic wave energy which is, in turn, radiated at a search area. In the search area, the ultrasonic wave energy strikes and reflected from an object. The reflected ultrasonic wave energy is converted into an echo signal which is, in turn, fed to a microcomputer. The microcomputer records and analyzes the echo signal so that it discriminates the distance between the sensor and the detected object and the property of the object.
However, ultrasonic sensors conventionally used are of the fixed type. Furthermore, they have an object-detecting orientation range of below 30.degree.. For detecting objects arranged in front over a lateral range of 180.degree., at least 6 ultrasonic sensors have been conventionally used. In other words, conventional object detecting devices are equipped with a plurality of ultrasonic sensors.
In the conventional object detecting devices with the above-mentioned construction, the function of detecting objects may be effectively achieved by the ultrasonic sensors. However, there is a disadvantage of an expensive construction due to the use of many ultrasonic sensors. In order to analyze the timing of a pulse signal and a corresponding echo signal reflected from an object, an expensive multiplexor should be also disposed at a path of a signal fed from each ultrasonic sensor. In particular, a larger space for occupying all the elements is required. As a result, it is difficult to design an object detecting device with a compact construction.
For solving these problems, there has been conventionally proposed a scanning device with a rotary type ultrasonic sensor capable of detecting objects arranged in front over a range of 180.degree.. FIG. 1 illustrates such a conventional scanning device. As shown in FIG. 1, the scanning device comprises an ultrasonic sensor 51 and a pair of coil springs 52 arranged above and beneath the ultrasonic sensor 51, respectively, and adapted to apply a return force to the ultrasonic sensor 51. A permanent magnet 53 is mounted the rear portion of ultrasonic sensor 51. At a rear wall 54 disposed in rear of the permanent magnet 53, a magnet coil 55 is mounted, which is spaced from the permanent magnet 53 and has an offset relationship with the permanent magnet 53. With this construction, the scanning device scans objects by utilizing the return force of the coil springs 52 and electromagnetic force generated between the permanent magnet 53 and the magnet coil 55 while rotating the ultrasonic sensor 51 laterally through an angle of 180.degree..
In the rotary type scanning device which is constructed to rotate the ultrasonic sensor utilizing a free vibration force of the coil springs, the coil springs may be deformed when a robot carrying the scanning device is inclined as it travels a slope or an irregular floor or rotates sharply. Such a deformation of coil springs causes the offset relationship between the magnet coil and the permanent magnet to be unstable. As a result, the scanning operation can not be performed until the coil springs return to their original states. In particular, the deformation of coil springs may also occur when the scanning device is subjected to an outer impact. Thus, the scanning device encounters a problem that the rotation cycle of ultrasonic sensor varies depending on environmental factors.
Since the ultrasonic sensor of the conventional scanning device operates while changing its linear orientation, its position for transmitting an ultrasonic wave signal does not correspond to its position for receiving an echo signal corresponding to the transmitted ultrasonic wave signal. As a result, there is a problem in detecting objects accurately.
The rotation cycle of ultrasonic sensor may be required to vary depending on its purpose for use. In the conventional scanning device, however, it is difficult to adjust the rotation cycle of ultrasonic sensor, because once the manufacture is completed, the elastic coefficient of the coil springs is fixed.